The automotive industry, for a number of years, has centered on the color grey, sometimes referred to as "neutral grey", as the aesthetic color of choice for automotive windows. At the same time, this industry, as well as the eyeglass art, have demanded that transmission in the UV and IR range of the light spectrum be minimized. This is also desirable at certain times in the architectural field. Governmental regulations in the automotive industry, moreover, simultaneously insist that the visible light transmittance be at least 70% or greater in certain, if not all, vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc., in the U.S.A.). A need is thereby created in these diverse industries for a glass which achieves these properties.
A glass window, windshield or other glass article is said to have the desirable color "grey", sometimes referred to as "neutral grey", if it manifests a dominant wavelength from about 435 nm, and preferably from about 470 nm, to less than about 570 nm, in combination with an excitation purity of less than about 4.5%. This, then, defines the meaning of the term "grey" as used herein. A still more preferred range of dominant wavelength, thus defining a more preferred "grey" as used herein, is about 480 nm-550 nm, and in like manner, a more preferred range of purity is about 0.2-4.5%. The appearance of such glass, thus defined, has been found to be of a truly "grey" color, rather than wandering into an objectionable hew of bronze, green or purple, or some other color. This "grey" color, as aforesaid, has found a unique demand in the automotive market, but it also has potential utility in the architectural and eyeglass markets as well.
At the same time that a true "grey" color is to be achieved, there is the usually required need to achieve rather strict levels of light transmission defined conventionally by:
LTa as visible light transmission, PA1 UV as ultraviolet light transmission, PA1 IR as infrared light transmission, and PA1 T.sub.s as total solar transmission. PA1 LTa, greater than about 70% PA1 UV, less than about 42%, preferably less than about 38% PA1 IR, less than about 37%, preferably less than about 28% PA1 T.sub.s, less than about 47%. PA1 a) a true "grey" color as defined above; PA1 b) a high transmittance of visible light, with an Lta usually equal to or greater than about 70%; PA1 c) a low IR transmittance less than about 37% and preferably less than about 28%; PA1 d) a low UV transmittance less than about 42% and preferably less than about 38%; and PA1 e) a low total solar transmittance less than about 47%. PA1 a) forming at least two separate prebatch mixes which when mixed together form an overall batch mixture comprising: PA1 b) mixing the first prebatch mix ingredients together separately from said remaining prebatch mix ingredients to form the first prebatch mix, PA1 c) mixing the remaining ingredients so as to form at least one other separate prebatch mix, thereafter, PA1 d) mixing the prebatch mixes together to form the overall batch mixture, PA1 e) melting the overall batch mixture to form a glass therefrom, and thereafter, PA1 f) forming the glass into the glass article.
In order to specify the parameters of these characteristics, it is generally necessary to specify the thickness of the glass which is the subject of the measurement. As used herein, in this respect, the term "a nominal thickness of about 1 mm-6 mm," and in certain embodiments, "about 3 mm-4 mm" means that the characteristics of the glass are those experienced when the thickness of the actual glass under investigation is adjusted for that nominal thickness range. Such thickness ranges, in this respect, are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as a recognized thickness range for the automotive industry.
When measured at the specified nominal thickness (e.g. 3.2 mm or 4 mm) the important characteristic of color achieved by this invention may be reported by the conventional CIE LAB technique (see U.S. Pat. No. 5,308,805). Such a technique is reported in CIE Publication 15.2 (1986) and ASTM: E 308-90 [Ill. C 2.degree. observer].
"Luminous transmittance" (LTa) [2.degree. observer] is a characteristic and term well understood in the art, and is used herein in accordance with its well known meaning [see U.S. Pat. No. 5,308,805]. This term is also known as Ill. A visible transmittance (380-780 nanometers inclusive), and its measurement is made in accordance with CIE Publication 15.2 (1986) and ANSI test method Z26.1.
"Total solar energy transmittance" (T.sub.s) (300-2100 nm inclusive, integrated using Simpson's Rule at 50 nm intervals using Parry Moon Air Mass=2) is another term well understood in the art [see U.S. Pat. No. 5,308,805]. It is used herein according to this well known meaning. Its measurement is conventional and well known.
The terms, and characteristics, of "ultraviolet light transmittance" (% UV), "infrared energy transmittance" (% IR), "dominant wavelength" (DW) and "excitation purity" (i.e. % "purity", or Pe) are also well understood terms in the art, as are their measurement techniques. Such terms are used herein, in accordance with their well known meaning [see U.S. Pat. No. 5,308,805].
"Ultraviolet transmittance" (% UW) is measured herein using Parry Moon Air Mass=2 (300-400 nm inclusive, integrated using Simpson's Rule at 10 nm intervals). Such a measurement is well known in the art.
"Infrared transmittance" (% IR) is conventionally measured using Simpson's Rule and Parry Moon Air Mass=2 over the wavelength range 800-2100 nm inclusive at 50 nm intervals. Such a measurement is well known in the art.
"Dominant wavelength" (DW) is calculated and measured conventionally in accord with the aforesaid CIE Publication 15.2 (1986) and ASTM: E 308-90. Its calculation and measurement are also well known in the art. As used herein, therefore, the term "dominant wavelength" includes both the actual measured wavelength and, where applicable, its calculated complement.
"Excitation purity" (Pe or % "purity") is measured conventionally in accord with CIE Publication 15.2 (1986) and ASTM: E 308-90.
For automotive windows (including windshields) it is desirable that the glass have the following characteristics (when measured at a nominal thickness of about 3 mm-4 mm and preferably at about either 3.2 mm or 4 mm as the particular situation may require), and often in the ultimate product as well:
Generally speaking, the prior art has at times been able to meet these automotive requirements, including the achievement of the necessary, aesthetic "grey" color by using as the essential ingredients of the colorant portion in an otherwise conventional silicate glass composition (e.g. a typical soda-lime-silica float glass composition), a combination of cobalt admixed with one or more of selenium, nickel, and cerium, along with an essential amount of iron. In many instances this combination was thought critical to achieving both a grey color and the requisite light transmission properties, or at least a "neutral bronze color." See, for example, U.S. Pat. Nos. 4,101,705; 5,061,659; 5,264,400; 5,318,931; 5,380,685; and Japanese Patent JP4-280834.
Unfortunately, these prior art combinations often had various problems associated with them. For example, cerium, being a well known UV absorber when present in glass in its reduced form, Ce.sup.3+, should be avoided for the following reason. Iron is conventionally introduced into glass in the form of Fe.sub.2 O.sub.3, part of which should be reduced to FeO to achieve the requisite low IR transmittance value. Cerium, which is introduced into glass in the form of CeO.sub.2, is known to oxidize divalent iron to trivalent iron either directly or by competition with any reducing agent present in the glass melt. Therefore, coexistence of iron oxide and cerium oxide will inevitably lead to a decrease in the concentration of FeO in the glass and thus will reduce its IR absorbing power.
The use of nickel in these prior art compositions presented the problem of nickel sulfide stones forming in the ultimate product. Selenium, furthermore, is difficult to retain in the glass during glass making. The loss of selenium created a difficulty in controlling the redox ratio in the glass, which ultimately adversely affected transmittance values. Without some, or all, of these aforesaid key ingredients, cobalt used by itself with the iron as the colorant portion of the glass composition, could not achieve the requisite combination of Lta and grey color as defined above.
Several attempts in the past have been made to employ the rare earth element erbium (reported conventionally as Er.sub.2 O.sub.3, and used herein according to this conventional practice) as a colorant in automotive windows and other glass articles. For example, the aforesaid U.S. Pat. No. 5,264,400 reports the use of such an ingredient in glasses of both bronze and grey tinted colors. However, as reported therein, the use of cerium oxide is an essential ingredient in the composition.
As another example, the aforesaid Japanese Patent No. 280834 employs Er.sub.2 O.sub.3 in a glass composition which is then said to have a "low thermal expansion coefficient." The glass employs from 10-20% B.sub.2 O.sub.3 and thus is properly referred to as a borosilicate glass, rather than the more conventional soda-lime-silica glasses used in automotive windows. While stating, in effect, that cobalt and nickel are optional, and no use of Se or Ce is reported, the dominant wavelength reported is accordingly rather high, i.e. from 570-610 nm, or tending toward an objectionable bronze color, even at the lower wavelengths achieved, rather than achieving a true "grey" color as defined above.
Reference to the examples presented in this Japanese Patent '834, moreover, demonstrates that to achieve the lower range of wavelengths (e.g. the lowest reported in 578 nm) the total iron content had to be kept at a very low 0.25% and the excitation purity was a very high 14.2%. This leads to the conclusion that this patent does not achieve, nor does it teach how to achieve, a true "grey" glass which, through the use of a high level of iron in the colorant portion (rather than the low level of iron used), also simultaneously achieves low UV and IR and high LTa transmittances, along with a true "grey" color. Indeed, in those examples which do not use cerium or some other UV absorber, and with the low levels of iron employed in those examples achieving lower dominant wavelengths, it is to be presumed that unacceptably high IR and UV transmittance values are the result.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving the requisite grey color and meets the other solar management requirements of the particular industry in which it is to be used. It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.